The making of a monolith
Amorphous calcium carbonate is a hard material that is difficult to make into large, clear blocks. It is also sensitive to heating, and compacting the starting nanoparticles too much tends to lead to crystallization. Mu et al. determined the optimal amount of water in amorphous calcium carbonate to create clear, solid monoliths through compression. The key is to regulate the amount of diffusion in the system so that particle boundaries fuse without triggering sample-wide crystallization. This fusion strategy may also work for similar amorphous inorganic ionic compounds.
Science, abg1915, this issue p. 1466
Abstract
Biological organisms can use amorphous precursors to produce inorganic skeletons with continuous structures through complete particle fusion. Synthesizing monoliths is much more difficult because sintering techniques can destroy continuity and limit mechanical strength. We manufactured inorganic monoliths of amorphous calcium carbonate by the fusion of particles while regulating structurally bound water and external pressure. Our monoliths are transparent, owing to their structural continuity, with a mechanical strength approaching that of single-crystal calcite. Dynamic water channels within the amorphous bulk are synergistically controlled by water content and applied pressure and promote mass transportation for particle fusion. Our strategy provides an alternative to traditional sintering methods that should be attractive for constructing monoliths of temperature-sensitive biominerals and biomaterials.